A typical automatic transmission (AT) includes a torque converter and a powertrain with a multiple speed gear mechanism connected to the torque converter. In addition, a hydraulic control system is provided for selectively operating at least one operational element included in the powertrain, according to the running state of a vehicle.
When it is determined that an upshift is required on the basis of vehicle speed and throttle valve opening, a transmission control unit (TCU) starts upshift control by starting control of a solenoid valve in the AT, which is usually called “shift-start point” and is abbreviated as “SS point”. By starting the solenoid valve control, after a certain period, an off-going frictional element begins releasing its hydraulic pressure, and an on-coming element begins to be supplied with a hydraulic pressure, which is usually called “shift-begin point” and is abbreviated as “SB point”. The period after the SS point to the SB point becomes a delay period which is not used for an actual shifting operation of the AT. Such a period after the SS point to the SB point is usually called a torque phase.
So, an actual shifting period (also called an inertia phase) of the AT begins at the SB point and finishes at a time point at which the off-going element is fully disengaged and the on-coming element is fully engaged. Such a time point at which the off-going element is fully disengaged and the on-coming element is fully engaged is usually called “shift-finish point” and is abbreviated as “SF point”. In this sense, such SB point is understood as an actual shift-begin point at which a shifting operation actually begins.
Generally a vehicle equipped with an AT starts moving forward or rearward by static shifting such as N→D or N→R shifting. Therefore, control of such static shifting is an important part in features of an AT. Regarding conventional duty control in such static shifting, adjustment of a duty begins after a predetermined fill time after an SS point, and the duty is decreased by a predetermined jumping amount at an SB point for enhancing shift feel.
FIG. 1 illustrates a duty control pattern for an on-coming frictional element in the case of a static N-D shifting according to the prior art, and a reducing jumping amount is adopted to enhance a shift feel related to an engagement of an on-coming frictional element. That is, adjustment of a duty begins after a predetermined fill time F after an SS point, and the duty is decreased by a jumping amount Dp at a shift-begin (SB) point for reducing a shift shock. According to such a duty control scheme during static shifting, the duty is controlled in the same manner regardless of whether an accelerator pedal is tipped in.
FIG. 2 illustrates a duty control pattern for an on-coming frictional element in the case of accelerator tip-in during static N-D shifting also according to the prior art. In the case of accelerator tip-in during static shifting, engine torque increases in response to the accelerator operation. Therefore, as shown in FIG. 2, the same duty jumping amount Dp is applied at the SB point to reduce the duty even though an accelerator is in a tip-in state during static shifting. Accordingly, a turbine speed abruptly increases due to an increased engine torque, and subsequently, the turbine speed abruptly decreases when a target shift-speed is engaged in the AT. Such abrupt changes in the turbine speed imply a shift shock.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.